The onset of EMT is one of the hallmarks of tumorigenesis, which involves a
complex cascade of multiple intracellular signaling pathways and extracellular
cross talk, its activation in cancer cells signifies a first step in
generation of usually fatal distant metastasis. Therefore, elucidating the
regulatory elements of EMT signaling is of great therapeutic value. GSK3β is a
multifunctional kinase implicated in EMT regulation as well as other
tumorigenic signaling pathways, such as Wnt signaling and glycogen metabolism.
One of the regulatory proteins of GSK3β is PKA, a kinase activated by cAMP.
Deregulation of cAMP/PKA signaling pathway is implicated in tumorigenic
metabolic reprogramming and EMT. PKA can inhibit GSK3β by direct
phosphorylation and this phosphorylation is facilitated by the AKAP GSKIP via
direct binding to PKA and GSK3β. Since GSKIP is able to regulate GSK3β
activity via PKA as well as PKA activity spatially and temporally, elucidating
GSKIP’s exact function in tumorigenesis is compelling. The principle cell
model for studying GSKIP’s function in this work was A549 lung carcinoma
cells. GSKIP Kd in A549 cells significantly inhibits cell migration without
affecting cell viability. In addition, GSKIP Kd results in a significant
increase in the protein expression levels of E-cadherin and a significant
decrease in protein expression levels of its transcriptional repressors,
ZEB1and SNAIL. A significant reduction in potent EMT inducers, such as TGFβ
and GPI/AMF and actin cytoskeleton regulator CD44, was also observed upon
GSKIP Kd. This modulation explains the reduced migration and indicates a role
of GSKIP in EMT regulation. In addition to its regulation of EMT, GPI/AMF
regulates metabolism and together with GSK3β’s and PKA’s intricate roles in
metabolic pathways, GSKIP’s role in metabolism was evaluated. The results show
that upon GSKIP Kd cells downregulate their dependence on mitochondrial energy
production via OXPHOS. This downregulation was attributed to reduced TCA cycle
flux due to reduced PDH activity. These results indicate that upon GSKIP Kd
A549 cells switch from catabolic metabolism, characterizing invasive cells, to
anabolic metabolism. In summary, the current research demonstrates for the
first time GSKIP’s involvement in EMT and metabolism regulation in cancer
cells, thus implicating GSKIP as a potential coupling agent between metabolic
reprograming of cancer cells and EMT, and proposes GSKIP as a potential
therapeutic target.